Speaker
Description
\documentclass[a4paper]{article}
\begin{document}
\begin{center}
\noindent The $^7$Be($n,p_1$)$^7$Li$^*$ reaction relevant to the cosmological lithium problem studied with the $^9$Be($^3$He,$\alpha$)$^8$Be($p$)$^7$Li and $^7$Li($^3$He,$d$)$^8$Be($p$)$^7$Li reactions\
\vspace{5mm}
N. Iwasa,$^1$ K. Ichimura,$^1$ S. Ishikawa,$^1$ S. Kubono,$^{2, 3}$ M. Egeta,$^1$ \
T. Haginouchi,$^1$ S. Ishio,$^1$, S. Matsue,$^1$ S. Numazawa,$^1$ K. Watanabe.$^1$ \
S. Sonoguchi,$^1$ T. Miyashita,$^1$ K. Nishio,$^4$ K. Hirose,$^4$ H. Makii,$^4$ \
R. Orlandi,$^4$ F. Suzaki,$^4$ J. Smallcombe,$^4$ S. Hayakawa,$^3$ and T. Kawabata$^5$
\
\vspace{5mm}
$^1${\it Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan.}\
$^2${\it RIKEN Nishina Center, RIKEN, Wako, Saitama 351-0198, Japan.}\
$^3${\it Center for Nuclear Study (CNS), the University of Tokyo,Wako, Saitama 351-0198, Japan}\
$^4${\it Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan.}\
$^5${\it Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan.}\
\end{center}
\noindent Abstract:
The primordial $^7$Li abundance observed in metal poor stars is known to be about one third of that predicted by the standard big bang nucleosynthesis (BBN) models.
This discrepancy is called ``the cosmological lithium problem'' and is one of the most important issues remained in BBN.
The questions are if (1) the BBN models correctly include all the nuclear reaction process,
(2) the astronomical observations correctly reflect the primordial $^7$Li abundance, or
(3) by other reasons like new physics beyond the standard model might be hidden.
From the point of the nuclear reaction process, since most of $^7$Li were immediately destroyed by the $^7$Li($p,\alpha$)$^4$He reaction,
the primordial $^7$Li was mainly synthesized by the electron capture of $^7$Be after the end of BBN epoch.
If the $^7$Be destruction reaction rate was large enough to reduce primordial $^7$Li abundance, then the present model would be validated without introducing any unknown physics.
The $^7$Be($n,p$)$^7$Li reaction is considered to be one of the most important $^7$Be destruction reactions.
However, the $^7$Be($n,p_1$)$^7$Li* (0.478keV, $\frac{1}{2}^-$) reaction was neglected in BBN except for the 2$^-$ state at 18.91 MeV in $^8$Be.
We have studied the $^7$Be($n,p_1$)$^7$Li$^*$ reaction by performing experiments to populate the resonant states at 18.9 - 20.1 MeV in $^8$Be by
the $^9$Be($^3$He,$\alpha$)$^8$Be$^*$ and $^7$Li($^3$He,$d$)$^8$Be$^*$ reactions and to measure decay protons to the ground and
first excited states in $^7$Li (called $p_0$ and $p_1$, respectively) [1].
The ($n,p_1$) contribution around BBN energy was found to be about 1 \%.
We are now studying $^7$Be destruction reactions by tritons by using transfer reactions.
The present status of the project will be also discussed.
\vspace{5mm}
\noindent
References: \
$[1]$ N. Iwasa {\it et al}., Phys. Rev. C{\bf 103}, 015801 (2021); N. Iwasa {\it et al}., Phys. Rev. C{\bf 112}, 035801 (2025).
\end{document}
| Category | Experiment |
|---|